1. Field of the Invention
The present invention relates to a method used in a wireless communication system and related communication device, and more particularly, to a method of constructing a spectrum map by using compressed sensing and related communication device.
2. Description of the Prior Art
A long-term evolution (LTE) system supporting the 3GPP Rel-8 standard and/or the 3GPP Rel-9 standard are developed by the 3rd Generation Partnership Project (3GPP) as a successor of a universal mobile telecommunications system (UMTS), for further enhancing performance of the UMTS to satisfy increasing needs of users. The LTE system includes a new radio interface and a new radio network architecture that provides a high data rate, low latency, packet optimization, and improved system capacity and coverage. In the LTE system, a radio access network known as an evolved universal terrestrial radio access network (E-UTRAN) includes multiple evolved Node-Bs (eNBs) for communicating with multiple UEs, and communicates with a core network including a mobility management entity (MME), a serving gateway, etc., for Non Access Stratum (NAS) control.
A LTE-advanced (LTE-A) system, as its name implies, is an evolution of the LTE system. The LTE-A system targets faster switching between power states, improves performance at the coverage edge of an eNB, and includes advanced techniques, such as carrier aggregation (CA), coordinated multipoint transmission/reception (COMP), UL multiple-input multiple-output (MIMO), etc. For a UE and an eNB to communicate with each other in the LTE-A system, the UE and the eNB must support standards developed for the LTE-A system, such as the 3GPP Rel-10 standard or later versions.
In addition to the advanced techniques mentioned above, the most effective way for improving quality of a received signal is to shorten a distance between a transmitter and a receiver in a wireless communication system. Thus, a heterogeneous network is proposed for introducing multiple layers of cells in the wireless communication system such that the distance between the transmitter and the receiver is shortened.
For example, there are three types of cells and a relay node in the heterogeneous network. According to coverage of the cells, the cells are a macrocell, a picocell and a femtocell from the largest to the smallest. Besides, the macrocell, the picocell and the femtocell are managed by a macro base station (BS) (e.g. eNB), a pico BS and a femto BS, respectively. Different from a convention network including only macrocells, the heterogeneous network not only includes the macrocells, but each of the macrocells could include at least one picocell, at least one femtocell and at least one relay node for improving throughput of UEs in the heterogeneous network. In this situation, a UE in coverage of a macrocell may also be in coverage of a picocell or a femtocell in the macrocell. If the UE is far from a macro BS of the macrocell, the UE can communicate with a pico BS of the picocell or a femto BS of the femtocell with low transmission power to access services such as Internet, TV broadcasting, etc. Even if the UE is not in the coverage of the picocell and the femtocell, the UE may also communicate with the macro BS via a relay node wherein channel quality between the UE and the relay node is better than that between the UE and the macro BS. That is, the relay node serves as a bridge between the UE and the macro BS, and forwards signals between the UE and the macro BS. In other words, the UE and the macro BS do not need to increase their transmission power greatly to communicate with each other. Therefore, power consumption of the UE and the macro BS can be reduced by using the pico BS, the femto BS or the relay node. Furthermore, throughput of the UE is increased since quality of the signals transmitted and received by the UE is improved due to a short distance between the UE and the pico BS, the femto BS or the relay node.
However, even though the power consumption of the UE and the macro BS is reduced, interference in the macrocell is increased since the pico BS and the femto BS may transmit and receive signals at the same time in an overlapped bandwidth and cause the interference to each other. Therefore, the interference should be mitigated or avoided such that the multiple BSs can operate regularly to realize benefit of the heterogeneous network efficiently.
For example, a BS of a cell can allocate radio resources to UEs in the cell according to geographic distribution of power intensity (e.g. signal strength) in the cell, to minimize interference suffered by the UEs. That is, a spectrum map revealing the geographic distribution of the power intensity in the cell should be available at the BS such that the BS can allocate the radio resources to the UEs according to the spectrum map. However, the spectrum map is established based on measurement reports transmitted by the UEs. If high accuracy is required for the spectrum map, sizes of the measurement reports should be large, and overhead caused by the measurement reports is very high. On the other hand, if the measurement reports are undersampled to reduce the overhead before transmitting to the BS, i.e., only part of the measurement reports are transmitted, the BS may not completely recover the measurement reports due to the Nyquist Theorem, i.e., information which is compressed or undersampled too much (e.g. over a certain threshold) can not be completely recovered without distortion. That is, some information of the measurement reports is lost, and distortion is caused to the spectrum map, i.e., accuracy of the spectrum map is low. Besides, when a number of the UEs may not be sufficient and/or positions of the UEs are not uniform enough, the measurement reports can also be seem as being undersampled. In other words, high accuracy of the spectrum map and low overhead caused by the measurement reports are hard to be achieved at the same time, and tradeoff must be made. Therefore, benefit brought from the interference mitigation and the interference avoidance is limited due to the tradeoff, and how to establish the spectrum map with high accuracy and reduced overhead is a topic to be discussed and addressed.